Bottom Line:
Illusory-conjunction errors result when an object is correctly identified but is combined incorrectly.Based on a subsequent error analysis for color and size, the results showed a significant increase in illusory conjunction errors for the PC lesioned rats relative to controls for color and relative to color discrimination, suggesting that the PC may support feature binding as it relates to color.There was an increase in illusory conjunctions errors for both the PC lesioned and control animals for size, but this appeared to be due to highly variable performance with size discrimination.

Affiliation: Department of Psychology, University of Utah, Salt Lake City UT, USA.

ABSTRACTWhen several different objects are presented, visual objects are perceived correctly only if their features are identified and then bound together. Illusory-conjunction errors result when an object is correctly identified but is combined incorrectly. The parietal cortex (PC) has been shown repeatedly to play an important role in feature binding. The present study builds on a series of recent studies that have made use of visual search paradigms to elucidate the neural system involved in feature binding. This experiment attempts to define the role the PC plays in binding the properties of a visual object that varies on the features of color and size in rats. Rats with PC lesions or control surgery were exposed to three blocks of 20 trials administered over a 1-week period, with each block containing 10-one feature and 10-two feature trials. The target object consisted of one color object (e.g., black and white) and one size object (e.g., short and tall). Of the 10 one feature trials, five of the trials were tailored specifically for size discrimination and five for color discrimination. In the two-feature condition, the animal was required to locate the targeted object among four objects with two objects differing in size and two objects differing in color. The results showed that the PC lesioned compared to control rats had difficulty in learning the one and two features components of the task and the rats also performed more poorly on the one vs. two feature components of the task. Based on a subsequent error analysis for color and size, the results showed a significant increase in illusory conjunction errors for the PC lesioned rats relative to controls for color and relative to color discrimination, suggesting that the PC may support feature binding as it relates to color. There was an increase in illusory conjunctions errors for both the PC lesioned and control animals for size, but this appeared to be due to highly variable performance with size discrimination. Overall these results suggest that the PC rats display performance errors that appear to be consistent with the notion of illusory conjunction errors.

Figure 2: Mean number of search errors for one or two features for control and parietal cortex lesioned rats as a function of blocks of trials. Each block consisted of 20 trials.

Mentions:
The results are shown in Figure 2 and indicate that for the control rats the mean percent correct performance improved across blocks of trials for both the one- and two-feature condition, but for the PC lesioned rats there was better performance for the one compared to the two-feature condition, but little improvement across blocks of trials. The analysis revealed a significant group effect [F(1, 10) = 8.26, p = 0.016], a significant blocks of trials effect [F(2, 20) = 5.67, p = 0.011], and a significant feature effect [F(1, 10) = 16.53, p = 0.002], but no significant interactions. These data suggest that PC rats make many errors resulting in impaired performance especially for both the one- and two-feature condition suggesting that they are susceptible to discrimination problems as well as the making of illusory conjunction errors.

Figure 2: Mean number of search errors for one or two features for control and parietal cortex lesioned rats as a function of blocks of trials. Each block consisted of 20 trials.

Mentions:
The results are shown in Figure 2 and indicate that for the control rats the mean percent correct performance improved across blocks of trials for both the one- and two-feature condition, but for the PC lesioned rats there was better performance for the one compared to the two-feature condition, but little improvement across blocks of trials. The analysis revealed a significant group effect [F(1, 10) = 8.26, p = 0.016], a significant blocks of trials effect [F(2, 20) = 5.67, p = 0.011], and a significant feature effect [F(1, 10) = 16.53, p = 0.002], but no significant interactions. These data suggest that PC rats make many errors resulting in impaired performance especially for both the one- and two-feature condition suggesting that they are susceptible to discrimination problems as well as the making of illusory conjunction errors.

Bottom Line:
Illusory-conjunction errors result when an object is correctly identified but is combined incorrectly.Based on a subsequent error analysis for color and size, the results showed a significant increase in illusory conjunction errors for the PC lesioned rats relative to controls for color and relative to color discrimination, suggesting that the PC may support feature binding as it relates to color.There was an increase in illusory conjunctions errors for both the PC lesioned and control animals for size, but this appeared to be due to highly variable performance with size discrimination.

Affiliation:
Department of Psychology, University of Utah, Salt Lake City UT, USA.

ABSTRACTWhen several different objects are presented, visual objects are perceived correctly only if their features are identified and then bound together. Illusory-conjunction errors result when an object is correctly identified but is combined incorrectly. The parietal cortex (PC) has been shown repeatedly to play an important role in feature binding. The present study builds on a series of recent studies that have made use of visual search paradigms to elucidate the neural system involved in feature binding. This experiment attempts to define the role the PC plays in binding the properties of a visual object that varies on the features of color and size in rats. Rats with PC lesions or control surgery were exposed to three blocks of 20 trials administered over a 1-week period, with each block containing 10-one feature and 10-two feature trials. The target object consisted of one color object (e.g., black and white) and one size object (e.g., short and tall). Of the 10 one feature trials, five of the trials were tailored specifically for size discrimination and five for color discrimination. In the two-feature condition, the animal was required to locate the targeted object among four objects with two objects differing in size and two objects differing in color. The results showed that the PC lesioned compared to control rats had difficulty in learning the one and two features components of the task and the rats also performed more poorly on the one vs. two feature components of the task. Based on a subsequent error analysis for color and size, the results showed a significant increase in illusory conjunction errors for the PC lesioned rats relative to controls for color and relative to color discrimination, suggesting that the PC may support feature binding as it relates to color. There was an increase in illusory conjunctions errors for both the PC lesioned and control animals for size, but this appeared to be due to highly variable performance with size discrimination. Overall these results suggest that the PC rats display performance errors that appear to be consistent with the notion of illusory conjunction errors.